The present invention generally relates to the preparation and manufacture of absorbent wiper materials. More particularly, the present invention relates to the preparation and manufacture of absorbent wiper materials that comprise split filaments and staple fibers.
It is known in the art that nonwoven materials of splittable thermoplastic filaments can be manufactured by a variety of processes. Generally, splittable thermoplastic filaments are produced by spinning two different polymers into a filament such that the two polymers form longitudinal heterogeneous cross-sections within the filaments. For example, side-by-side configurations may be formed in which the first polymer forms one side of the filament and the second polymer forms the other side. Many other configurations such as sheath-core or islands-in-the-sea are known in the art.
The filaments containing the longitudinal heterogeneous cross-sections can be split according to a variety of mechanisms described in the art. By way of example, U.S. Pat. No. 5,759,926 to Pike et al. discloses a mechanism whereby fibrillation is induced by contacting the filaments containing the longitudinal heterogeneous cross-sections with hot water. Mechanical agitation and differential shrinkage are additional mechanisms that may be employed. As further examples, U.S. Pat. No. 3,485,706 to Evans, U.S. Pat. No. 5,355,565 to Baravian, and U.S. Pat. No. 6,200,669 to Marmon et al. each disclose processes whereby unitary multicomponent fibers are split by a hydroentangling process that separates the individual segments of the unitary multicomponent fibers into microfibers.
It is also known in the art that staple fibers can be added to a nonwoven web to enhance absorbency. There are a variety of methods known to incorporate pulp fibers into the nonwoven fiber matrix. U.S. Pat. No. 4,818,464 to Lau and U.S. Pat. No. 4,100,324 to Anderson et al. describe coform processes that incorporate pulp fibers into meltblown fibers via an air laying process. U.S. Pat. No. 4,902,559 to Eschwey et al. discloses a process for the production of an absorbent nonwoven material formed of randomly distributed thermoplastic endless filaments which contain embedded hydrophilic or oleophilic staple fibers. U.S. Pat. No. 5,389,202 to Everhart et al. and WO00/29657(Haynes et al.) both describe a process of hydroentangling pulp fibers into a continuous filament nonwoven web. With regard to WO00/29657(Haynes et al.), a process is disclosed whereby pulp fibers are entangled into a matrix of splittable filaments followed by splitting of the filaments to entrap the pulp fibers. However, such process can result in incomplete splitting of the filaments due to the pulp fibers shielding the splittable filaments from the water jets.
There remains a need for a soft, strong, and absorbent nonwoven material and a process for making such a material. More specifically, there remains a need for an efficient and effective process to produce composites of staple fibers and low denier continuous filaments.
The present invention comprises a method of forming a nonwoven composite fabric that includes a) providing a first layer that includes splittable continuous fibers, b) splitting at least a portion of the splittable continuous fibers into split filaments, c) thereafter superposing a second layer and the first layer, wherein the second layer includes staple fibers, and d) entangling the first and second layers to form a composite fabric. Desirably, the split filaments are substantially continuous in length.
In one aspect, the splitting step may comprise impinging the splittable continuous fibers with high energy jets such as, for example, high energy water jets. In a further aspect, the entangling step may include impinging the superposed first and second layers with high energy jets such as, for example, high energy water jets. The high energy jets of the entangling step are desirably directed at the exposed surface of the second layer. Desirably, the entangling jets are supplied through first orifices, the hydraulic pressure at the first orifices ranging from about 2,500 kPa to about 21,000 kPa. Desirably, the splitting jets are supplied through second orifices, the hydraulic pressure at the second orifices ranging from about 1,300 kPa to about 14,000 kPa. In an even further aspect, the hydraulic pressure at the second orifices is lower than the hydraulic pressure at the first orifices.
The composite fabric produced by the method of the present invention may include a staple fiber rich side. Alternatively, the composite fabric produced by the method of the present invention may be characterized by staple fibers that are entangled substantially uniformly throughout the cross section of the composite fabric.
The method of the present invention desirably produces a composite fabric wherein at least about 25% of the splittable continuous fibers are at least partially split. Still more desirably, the method of the present invention produces a composite fabric wherein at least about 50%, 75%, 90, or even 95% of the splittable continuous fibers are at least partially split. In one embodiment of the present invention, the entangling step optionally does not result in substantial additional splitting of the splittable continuous fibers.
In a further aspect, the multicomponent fibers are desirably selected to split in a manner such that the split filaments have a denier of less than about 0.7, and still more desirably, a denier of less than about 0.1, and even more desirably, a denier of less than about 0.01.
In a further aspect the splittable continuous fibers of the present invention include spunbond fibers. The spunbond fibers desirably include a first thermoplastic polymer and a second thermoplastic polymer arranged in distinct zones across the cross-section of the fibers wherein the first and second thermoplastic polymers are incompatible with each other. Further, the staple fibers of the present invention desirably include pulp fibers.
In a further aspect, the ratio of the dry weight of the first layer to the dry weight of the second layer desirably ranges from about 0.05 to about 9, more desirably, from about 0.1 to about 2, and even more desirably, from about 0.2 to about 1.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments.